//起始时间
//1980年1月1日星期二
//前面有两个空位
//一年有365天 366天
//需要算出今年是365还是366

var year = 2019;
var month = 6;


document.querySelector("#nian").innerHTML = year;
document.querySelector("#yue").innerHTML = month;

//总天数
var days = 0;

//判断这一年是不是闰年
function runNian(y){
    if(y % 400 === 0 || (y % 4 === 0 && y % 100 != 0)){
        return true;
    }else{
        return false;
    }
}



//算1980年到现在的头一年有多少天
for(var i = 1980;i<year;i++){
    if(runNian(i)){
        days += 366;
    }else{
        days += 365;
    }
}


//今年的1月到这个月的上一个月有多少天
//31
//28
//31
//30

for (var k = 1;k< month;k++){
    switch(k){
        case 1:
            days += 31;
            break;
        case 2:
            if (runNian(year)){
                days += 29;
            }else{
                days += 28;
            }
            break;
        case 3:
            days += 31;
            break;
        case 4:
            days += 30;
            break;
        case 5:
            days += 31;
            break;
        case 6:
            days += 30;
            break;
        case 7:
            days += 31;
            break;
        case 8:
            days += 31;
            break;
        case 9:
            days += 30;
            break;
        case 10:
            days += 31;
            break;
        case 11:
            days += 30;
            break;
        case 12:
            days += 31;
            break;
    }
}

//算一下本月一共有多少天
var day = 0;
switch (month){
    case 1:
        day += 31;
        break;
    case 2:
        if (runNian(year)){
            day += 29;
        }else{
            day += 28;
        }
        break;
    case 3:
        day += 31;
        break;
    case 4:
        day += 30;
        break;
    case 5:
        day += 31;
        break;
    case 6:
        day += 30;
        break;
    case 7:
        day += 31;
        break;
    case 8:
        day += 31;
        break;
    case 9:
        day += 30;
        break;
    case 10:
        day += 31;
        break;
    case 11:
        day += 30;
        break;
    case 12:
        day += 31;
        break;
}

console.log(day);




//算一下上个月一共有多少天
var prevDay = 0;
switch (month - 1){
    case 1:
        prevDay += 31;
        break;
    case 2:
        if (runNian(year)){
            prevDay += 29;
        }else{
            prevDay += 28;
        }
        break;
    case 3:
        prevDay += 31;
        break;
    case 4:
        prevDay += 30;
        break;
    case 5:
        prevDay += 31;
        break;
    case 6:
        prevDay += 30;
        break;
    case 7:
        prevDay += 31;
        break;
    case 8:
        prevDay += 31;
        break;
    case 9:
        prevDay += 30;
        break;
    case 10:
        prevDay += 31;
        break;
    case 11:
        prevDay += 30;
        break;
    case 12:
        prevDay += 31;
        break;
}

console.log(prevDay);

//因为19800101是从星期二开始的，我想让它从星期日开始算，所以
days += 2;


console.log(days);


//算出本月的1号是星期几（算出起始的位置）
var start = days % 7;
console.log(start);



//算一下当前页面的日历一共可以放多少天
var num = 42;

//前面空有多少个

//本月有多少天？

//下一个月有多少天  8天  一共有45天-上个月的3天-这个月的天数=下个月的天数
var nextDays = num - start - day;


//取到今天是几号？
var thisdate = new Date().getDate();

var date1 = document.querySelector("#date1");

for (var j = prevDay - start + 1;j <= prevDay;j++){
    date1.innerHTML += "<span class='h'>" + j + "</span>";
}


for (var a = 1;a <= day;a++){
    if(a == thisdate){
        date1.innerHTML += "<span class='today'>" + a + "</span>";
    }else{
        date1.innerHTML += "<span>" + a + "</span>";
    }
    
}
for (var s = 1;s <= nextDays; s++){
    date1.innerHTML += "<span class='h'>" + s + "</span>";
}


//思路
//1.先算1980-2018年一共有多少天

//2.再算2019年1月 - 4月一共多少天

//3.再算本月一共有多少天

//4.根据余数算出前面有几个空位

//5.补充末尾有几个空位，用for循环补充上